As economic confidence has ebbed over the past week, there's a sense of an era drawing to a close. And with that comes a reckoning of what's been achieved and what opportunities have been missed. It's a conversation which looks back not forward: what we have done, what the Tories didn't do, rather than what we are going to do. It's a dangerous symptom of the fatalism which several fringe speakers such as the outspoken MP Fiona Mactaggart are warning against.

But however dangerous the reckoning, it throws an interesting light on New Labour. The perspective of history is always, subtly and powerfully, different from the snap judgments of the day – it is the one, after all, which lasts.

So into the balance go the much cited achievements in early years provision. Also winning credit are Labour's reforms on the constitution, praised by political historian David Marquand during the party conference as perhaps the most significant of any government in several centuries: devolution, the human rights act, directly elected mayors, some Lords reform.

But set against these historic achievements comes the bitterness of opportunities missed. The one which is already haunting the Labour party is that they should have gone for electoral reform when they had the chance. If they had fulfilled their 1997 manifesto commitment, they could have truly transformed British political culture. But with the hubris of big majorities, they binned the commitment, complacently assuming they could carry on winning with first past the post. Now, as they stare crushing defeat in the face, they feel keenly the wisdom of their own argument in past years: that big majorities are not just bad for democracy – because they don't represent accurately the country's vote – but they are bad for the party, falsely bolstering a supremacy which can dramatically disintegrate.

There is a strong inclination, as Peter Hain and Mactaggart suggested in Manchester, for a last minute dash. Get some measure of electoral reform – any type will do – in place now before it is too late. There is the sharp realisation that if Brown had gone to the country a year ago with a manifesto commitment to electoral reform, Labour could have been in power for another decade. The fear is that this is the missed chance which will loom over the years in opposition.

Another equally powerful sense of missed opportunity in Brown's coinage of the phrase "progressive consensus" despite never managing to define it successfully, nor own this agenda. Now Labour sees this home territory subjected to baffling Tory inroads.

"Progressive" is the word which both the Tories and Labour are now squabbling to define and own. It's not just a matter of rhetoric and semantics: it is a highly charged word in British politics, which has been used to distinguish the two parties for much of the last century. The left believed in progress, while the right was sceptical that such a thing was possible and believed that politics should have a more modest aim of continuing tradition and managing change.

But Labour's faith in progress has faltered in the face of a global capitalism it only hopes to moderate, rather than transform. Its own utopian dreams of progress towards a socialist future have been abandoned. At the same time, the Conservatives under Thatcherism became a party of radical change – which some called progress.

"Progressive" has become a "Humpty Dumpty word", as David Marquand put it to me during the conference: it means whatever you want it to mean. Empty of any real content, it's simply a word to claim superiority. It joins a dustbin of political terms like modernisation which have been overused, overextended and so badly exploited for political purposes that they no longer have meaning.

The reason why this matters is that Labour has dreamed for several decades that power would enable it to embed social democracy so deeply into the country that it would be hard to reverse. What they wanted was permanent change, and what they are realising is that huge ambition was probably within their grasp at key moments through their past decade in power but it slipped between their fingers. The recriminations over why that happened will be fearsome.